1、查看raw.githubusercontent.com的ip地址

可以在Hostname Summary查看raw.githubusercontent.com的ip地址.如图

2、配置host文件

sudo gedit /etc/hosts

加入

185.199.110.133 raw.githubusercontent.com
185.199.110.133  raw.github.com

以上步鄹可以解决如下问题

ERROR: cannot download default sources list from:
https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
Website may be down.

2.1 执行rosdep init

rosdep init

*当rosdep init以后在rosdep update过程中会遇到下载问题

3、修改sources.list.d的访问方式

3.1 使用wget下载需要的文件

wget https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml
wget https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml
wget https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml
wget https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml
wget https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml 
wget https://raw.githubusercontent.com/ros/rosdistro/master/melodic/distribution.yaml
 wget https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml

3.2 改变sources.list.d中的下载方法

# os-specific listings first
yaml file:///home/lvrobot/osx-homebrew.yaml osx

# generic
yaml file:///home/lvrobot/base.yaml
yaml file:///home/lvrobot/python.yaml
yaml file:///home/lvrobot/ruby.yaml
gbpdistro file:///home/lvrobot/fuerte.yaml fuerte

# newer distributions (Groovy, Hydro, ...) must not be listed anymore, they are being fetched from the rosdistro index.yaml instead

3.3 修改osdep2/sources_list.py

在 sources_list.py中加入

import ssl
ssl._create_default_https_context = ssl._create_unverified_context

以上可以解决rosdep update下载问题

4、执行

rosdep update

• 切记要多次尝试